Forging is a metal shaping process by application of compressive forces. Forging can be classified into hot, warm and cold forging according to the temperature at which is performed. Hammers or presses are used to deform the metal/alloy into high strength parts. Mechanical properties of the metal/alloy are improved by forging as it refines its grain structure, making it tougher and stronger. Following is a comparison of cold and hot forging process.
Cold Forging Process
The cold forging is performed at room temperature. The job-piece is compressed between two dies until it has assumed their shape.
Advantages of Cold forging
- Very little or no finishing work is required in Cold forged, which saves cost.
- High precision.
- High production rates
- Long die life
Cold Forging Disadvantages
- Only simple shapes in high volumes can be shaped
- Not suitable for customised components
- Low ductility
- Residual stress may occur.
Hot Forging Process
Hot forging process is performed at extreme high temperature (up to 1100°C for steel, 360°C to 520°C for Al-alloys, 700°C to 800°C for Cu-alloys). These temperatures are necessary in order to avoid strain hardening of the metal during deformation.
Hot Forging Advantages
- Good ductility
- More flexible than cold forging, thus customized parts can be manufactured.
- Excellent surface quality
Hot Forging Disadvantages
- Less precise dimensional tolerance.
- Careful monitored cooling process to be performed
- Risk of warpage
- Risk of job piece and atmosphere reactions
Hot Forging vs. Cold Forging: Conclusion
Strengthening mechanism in cold forging is strain hardening, while at high temperature during hot forging, strain hardening is avoided resulting in optimum yield strength, low hardness and high ductility. The process delivering desired quality more economically is chosen. The decision is based on the required properties of the desired component, its cost of production and customer’s requirements.